AWV
MANUFACTURING THE
AWV
TRANSISTOR
Reproduced from a publication of the Amalgamated Wireless Valve Company Pty Ltd 1958. The method described here is remarkably similar to that used by Mullard in their publication Manufacture of Junction Transistors. The common link is RCA: both companies had RCA licenses.
These photographs, taken in the Rydalmere, NSW, factory of AWV, show the main processes in the manufacture of the AWV germanium alloyed junction transistor, in step-by-step operations leading to the final product. In order to ensure that the transistor will meet the demands made upon it, every step in the manufacture must be strictly controlled.
The stringent controls employed in the AWV factory fall into two main types. Firstly, there is careful examination and testing of all raw materials and components to make sure that no material or parts which are not of the required quality reach the assembly area. Secondly, tight controls and manufacturing limits are imposed on the manufacturing operation, coupled with close inspection and testing at every stage. No transistor or part proceeds to the next operation unless it has been tested and found to comply with the specifications laid down.
The photographs tell the story of this fascinating operation in a beautiful air-conditioned factory. The comfortable working conditions and the almost clinical cleanliness observed in the illustrations show how no effort has been spared to produce a consistently high-grade and reliable product.
STEP 1: The germanium is received in ingot form, and before it is used in manufacturing is subjected to a number of quality checks. Among the qualities tested is the resistivity (the electrical resistance) of the crystal, to check the impurity concentration of the grown crystal. The higher the resistivity, the purer the material.
STEP 2: The next stage is to cut the germanium crystal into slices. Great care must be taken in this process, as improper slicing will impair the quality of the transistor. The slicing is done by means of a diamond edged saw. The table on which the ingot is held allows minute adjustment of the piece and therefore the angle of cut with reference to the crystal plane. The thickness of a slice is between 10 and 12 thousandths of an inch in a typical case.
STEP 3: The thickness of the germanium slices must be controlled within fine limits. In order to achieve this, the slices are lapped. This process consists of placing the slices on a rotating table spread with an abrasive compound; here they are lapped or abraded between the lower circular table and the upper orbitally rotating weighted discs. In addition to reducing the thickness of the slices, this process imparts an extremely fine finish to the slices. Lapped thickness is between 7 and 9 thousandths of an inch in a typical case.
STEP 4: An acid etch is then used to bring the slices to a finished thickness. Here the slices are put in a polythene beaker and etched with a solution of hydrofluoric acid. This process facilitates extremely fine control of the thickness and also imparts a high luster to the slice. The etched thickness is between 35 and 60 ten-thousandths of an inch, depending on the type of transistor being made.
STEP 5: Having reduced the germanium slices to the required thickness, the next step is to cut the slices into the small squares or rectangles which will eventually form the base region of the transistor. This is done by placing the slices onto a perforated table, where they are firmly held by suction. They are then cut be scribing them with a diamond tipped tool. Here again, the machine is capable of very fine adjustment.
STEP 6: The germanium dice are then measured for thickness by passing them through a roller micrometer. This machine automatically feeds and sorts the dice into thickness groups and collects them in the plastic tubes attached to the front of the machine. Each group is measured to a tolerance of plus or minus 50 millionths of an inch. A typical dice size is 1/16th of an inch square, by 2 thousandths of an inch thick, a shade thicker than cigarette paper.
STEP 7: Here the base tab, the germanium dice and the emitter and collector dots are inserted into a graphic jig. The type of emitter and collector dots used determine whether the finished transistor is p-n-p or n-p-n type. The jigs are placed in a conveyer furnace where the emitter and collector dots alloy with the germanium dice, which at the same time is fused to the base tab.
Footnote: Other sources (Watt History) contradict this, stating that the collector dot was alloyed in a first pass through the alloy furnace and the emitter dot alloyed in a second firing. The Mullard process also used two furnace passes to complete alloying.
STEP 8: The base tab assembly is now spot-welded to the stem or transistor base. Two nickel wires 5 thousandths of an inch in diameter are also spot-welded to the emitter and collector dots. These delicate operations are performed with the aid of a large illuminated magnifier.
STEP 9: A binocular microscope is used to position the emitter and collector lead wires between the stem leads and the emitter and collector dots of the alloyed germanium dice. This picture is a good example of the almost clinical cleanliness observed throughout the operation.
STEP 10: Assembly of the transistor is now complete except for encapsulation. A further acid etch now takes place on the complete assembly to bring the characteristics within the necessary limits. This etch is a delicate operation, and a constant check is kept on the electrical characteristics during the whole time. This etch is followed by a prolonged cascade wash in ultrapure water to remove all traces of acid, followed by a thorough hot-air drying off.
STEP 11: The active regions of the etched transistors are encapsulated in a silicone resin and placed in an oven for curing of the resin and stabilization of the characteristics. This is done to ensure that the parameters will remain constant and that the completed transistors will have a long and satisfactory life.
STEP 12: In the operation shown here, the outer cases of the transistors are being filled with a measured quantity of a viscous non-conductive substance. This material acts as a protective coating for the active part of the transistor when finally assembled.
STEP 13: Final assembly of the transistor takes place here, where the stem unit, to which the base tab assembly has been mounted and connected, is hermetically sealed in the outer case. This critical operation is carried out in a controlled and dust free environment in a glass fronted and pressurized cabinet. The operator’s hands and arms are inserted into long sleeved rubber gloves which form an integral part of the cabinet.
STEP 14: Final testing. Each transistor is carefully tested to ensure that all specifications are met. It is largely upon the standards set here that the production of a high grade and consistent product depend, and rigid limits are set down. Here also the “family groups” of transistors are sorted by testing routines into groups representing the various commercial type numbers of each group.
STEP 15: When the transistor has passed all tests satisfactorily, it is branded with the well known AWV monogram and the commercial type number. The branding also includes a manufacturing code for control purposes.
